actar from GBATEMP has released an application called WiiCoverDownloader, here is a quote from his thread:
– PC with .NET 2.0 installed
– Your device with games and loader
One time selected the devices with your loader and your games, the application will download the covers in the correct folder (automatically if default and not customized).
You can download covers for WiiGames, WiiWare, VirtaulConsole, GameCube games.
You can customize your path or languages if you want.